Chemistry Paper 3 with Confidential Questions and Answers - Lanjet Joint Mock Exams 2020

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INSTRUCTIONS TO CANDIDATES

  • Write your name and index number in the spaces provided.
  • Sign and write the date of examination in the spaces provided on the question paper.
  • Answer ALL the questions in the spaces provided in the question paper.
  • You are NOT allowed to start working with the apparatus for the first 15 minutes of the 2¼ hours allowed for this paper. This time is to enable you to read the question paper and make sure you have all the chemicals and apparatus you need.
  • Mathematical tables and silent electronic calculators' may be used.
  • All working must be clearly shown where necessary.

 

  1. You are provided with;
    1. Solid A magnesium ribbon
    2. Solution B 2MHCL
    3. Solution C, 0.3MNaOH
    4. Distilled water

      You are required to determine the:
      1. Temperature change when magnesium reacts with excess hydrochloric acid
      2. Number of moles of hydrochloric acid that remains unreacted
      3. Number of moles of magnesium that reacted
      4. Molar heat of reaction between magnesium and hydrochloric acid

Procedure 1
Using a burette, measure 50cm of solution B and place it in 100ml beaker. Measure the temperature of solution B in 100ml beaker after every 10 seconds. At 30th seconds add magnesium ribbon to solution B and continue recording the temperature. Stir the mixture continuous with a thermometer making sure that the magnesium ribbon remains in the solution as it reacts. Measure the temperature after ever 10 seconds and record values at the table below. Continue stirring and measure the temperature to complete table 1 below.
Keep the resulting solution for use in procedure 2.
Table 1

Time (sec) 0 10 20 30 40 50 60 70 80 90 100 110 120 130
Temperature (ºC)        X                    

  1. Plot graph of temperature against time on the grid provided. (3mks)
    3
  2. On the graph, show the maximum change in temperature ∆T and deter mine its value.

    Procedure 2
    Transfer all the solution obtained in procedure 1 into 250ml volumetric flask. Top up with distilled water to 250ml mark. Label it with solution D. Empty the burette and fill it with solution C. Pipette 25mlof solution D and place it in 250ml conical flask. Add drops of phenolphthelene indicator and titrate solution C against solution D. Record the results in table 2. Repeat the titration of solution C against solution D and complete table 2.
    Table 2 
    b) 
  I II III
Find burette reading      
Initial burette reading      
Volume of solution C(cm3)      
    (4mks)
  1. Calculate average volume of solution C used. (1mk)
  2. Calculate the number of moles of:
    1. 0.3MNaOH (1mk)
    2. Hydrochloric acid in 25cm3 of solution D. (1mk)
    3. Hydrochloric acid in 250cm3 of solution D. (1mk)
    4. Hydrochloric acid in 50cm3 of solution B. (1mk)
    5. Hydrochloric acid that reacted with magnesium. (1mk)
    6. Magnesium that reacted. (1mk)

c) Using your answer in iv above, determine molar heat of reaction between magnesium and hydrochloric acid. Assume the heat capacity of solution is 4.2Jg-1k-1 and density of solution 1g/cm3.  (2mks)

2. You are provided with solid E. Carry out the experiments below. Write your observation and inferences in the space provided.Using your answer in iv above, determine molar heat of reaction between magnesium and hydrochloric acid. Assume the heat capacity of solution is 4.2Jg-1k-1 and density of solution 1g/cm3. (2mks)

  1. Place all solid E in a boiling tube. Add about 20cm3 distilled water and shake until all the solid dissolves label this solution E. use solution E for experiments (i) and (ii)
  1. To 2cm3of solution E in a test tube in each of experiments I,II,III and IV add:
    1. Two drops of aqueous sodium sulphate;
       Observations  Inferences
      (1mk) (1mk)
    2. Five drops of aqueous sodium chloride;
       Observations  Inferences
      (1mk) (1mk)
    3. Two drops of barium Nitrate;
       Observations  Inferences
      (1mk) (1mk)
    4. Two drops of lead (ii) Nitrate
       Observations  Inferences
      (1mk) (1mk)
  2.  To 2cm3 of solution E in a test tube add 5 drops of aques sodium hydroxide. Add a piece of Aluminium foil provided to the mixture and shake. Warm the mixture and test any gas produced with the and read litmas papers.
     Observations  Inferences
    (2mk) (1mk)

3. You are provided with solid F. Carry out the following tests and record the observations and inference in the space provided.

  1. Place about one third of the solid F on a clean metallic spatula and burn it in a Bunsen burner flame.
     Observations  Inferences
    (1mk) (1mk)
  2. Place the remaining amount of solid F in a boiling tube. Add about 10cm3of distilled water and shake use the mixture for tests (i) to (ii)
     Observations  Inferences
    (½mk) (½mk)
    1. Using about 2cm3 of the mixture in a test tube determine the PH Using universal indicator paper and chart.
       pH  Inferences
      (1mk) (1mk)
    2. To about 2cm3 of the mixture in a test tube add three drops of acidified potassium manganese vii.
       Observations  Inferences
      (1mk) (1mk)
    3. To about 2cm3 of the mixture in a test tube add two or three drops of bromine water.
       Observations  Inferences
      (1mk) (1mk)

LANJET CLUSTER JOINT MOCK EXAM
CONFIDENTIAL

In additional to the fittings and Chemical found in the lab each candidate will require the following.

  1. Solid A. 17cm long magnesium ribbon
  2. 80cm3 of solution B
  3. 120cm3 of solution C
  4. 1g of solid E in a container
  5. 0.5g of solid F in a container
  6. About 500cm3 of distilled water.
  7. One 25ml pipette
  8. One 50ml burette
  9. One 100ml plastic beaker
  10. Thermometer (-100c to 1100c )
  11. Stop watch
  12. Two 250ml conical flask
  13. One 250ml volumetric flasks
  14. 6 dry test tubes in rack
  15. Two boiling tubes
  16. One metallic spatualla
  17. One piece each of red and blue litimus paper
  18. Piece of universal indicator paper
  19. Label
  20. About one cm2 Aluminum foil.

Access to

  1. Phenolphthalein indicator supplied with a dropper.
  2. Bunsen burner
  3. Universal indicator and PH chart
  4. 2M sodium hydroxide supplied with a dropper
  5. Barium Nitrate supplied with a dropper
  6. Acidified potassium magnate (vii) supplied with a dropper
  7. Freshly prepared bromine water supplied with a dropper
  8. 0.5M sodium sulphate supplied with a dropper
  9. 0.5M sodium Chloride supplied with a dropper.
  10. 0.5M lead (ii) Nitrate

Preparations

  1. Solid A is 0.4g of Mg exactly 17cm long. Mg ribbon
  2. Hydrochloric acid solution B is prepared by adding 172cm3 of concentrated hydrochloric acid
    of specific gravity 1.18gcm-0 to 500cm3 of distilled water in one litter volumetric flask then adding distilled water to the mark. Label this as solution B.
  3. Solution C made of adding 12g of NaOH pellet in 200cc of distilled water, stir then top it up in 1000ml volumetric flask.
  4. Acidify potassium mangate (vii) prepared by dissolving 3.2g of potassium manganate vii in 200cm3 of 2M sulphuric acid in 1L volumetric flask then adding water to the mark.
  5. Barium Nitrate prepared by dissolving 26g of barium Nitrate in 800cm3 of distilled water then topping up to 1L.
  6. Solid E is about 1g of barium Nitrate.
  7. Solid F is 0.5g Malleic acid.



MARKING SCHEME

  1.      
    1. Table 1
      Complete Table CT✓
      Trends Td ✓
      Decimal (D) ✓
      Decimal- consistence in use of decimal on temperature readings 0.0,0, 0.5
      Trends – constant, steady rise, constant then drop.
      Complete table – if a candidate has filled the table a ward full mark.
      1. Labelling and axis LA.✓½
        Plots (p) ✓
        Scale (s) ✓½
        Extrapolation (ex)✓
      2. T2-T1 = ΔT✓
        Highest temperature on extrapoliated graph
    2.    
      1. Complete table CT✓
        Decimal D ✓
        Accuracy (A) ✓±0.1✓
        ± 0.2✓½
        Beyond ± 0.2 award 0mrk
        Principles of averaging (P.A)✓
        Values averaged must be within ± 02 of each.
        Find answer F.A✓
      2. Molarities X titre value✓½
                     1000
        Correct answer ✓½
        1. Moles ratio 1:1✓½
          Answer in I ✓½
        2. Answer in II x 250 ✓½
                      25
          Correct answer ✓½
        3. Molarities acid x 50
                  1000
          Correct answer ✓
        4. Answer in IV – answer in III
          Correct answer ✓
        5. Moles ratio 1:2 ✓½
          Answer in V/2
          Correct answer✓½
          CΔH = McØ
          =50 x 4.2 x ΔT.✓
          = Correct answer ✓
           Answer in C 
          Answer in VI
          NB penalize ½ for missing sign and wrong unit.
  2.    
    1. White precipitate formed ✓
      Ca2+(Present.)
      Ba2+ (Present.)
      Pb2+ (Present.)

      (All = ✓
      2 =✓½
      1 = 0)

      1. NO white precipitate ✓
        Pb2+ (Absent ✓½)
        Ca2+(Present✓½)
        Ba2+ (Present✓½)
      2. No white precipitate✓
        SO42- (Absent)
        SO32- (Absent)
        CO32-(Absent)

        (3 = ✓
        2 = ✓½
        1 = 0)
      3. No white precipitate.
        Cl - Absent
        SO42-Absent
        ignore SO32- Absent
        CO32-Absent
    2. Shining aluminum foil dissolves forming grey solution✓ NO3- presents
      Gas produce turn red litimus paper blue
      Blue litmus remain blue✓
  3.    
    1. Burns with yellow sooty/ smoky flame✓
      1
    2. Solid dissolves on colorless solution ✓½
      Polar compound ✓½
      Polar organic substance.
      1. PH3✓ strong acidic solution ✓
      2. Purple potassium manganate vii turns colorless.✓
        Reject strong acid.
        2
        Reject solution turn colorless
        R - OH✓½ Present
      3. Orange bromine water turn colorless
        1
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